Despite advances in vehicle safety technology vehicle brakes remain a common cause of accidents and mechanical breakdowns. Fatal tractor trailer accidents cost Americans more than $20 billion every year and one person is killed or injured in a truck accident every 16 minutes. According to a recent study by the United States Department of Transportation (DOT) almost 30% of all commercial truck accidents involve brake failure and roadside inspections fail on average 15% of all trucks and buses inspected due to brake-related violations. Mechanical breakdowns cost additional time and money in unplanned repairs and vehicle downtime.
There are many potential problems with brakes in addition to normal brake component wear. Uneven wear, warping, and polishing of components can occur due to mismatched components, debris between fiction surfaces, and misalignments during installation. Friction surface cracks, breakage, and delamination can occur suddenly without warning. Overheating and heat checking can be caused by overloaded vehicles and excessive and sudden braking. Contamination and corrosion of braking components can occur due to fluid leaks or road surface treatment chemicals. Braking imbalances can be caused by air system valve problems and occur in many locations such as tractor versus trailer, axle versus wheel-end, and driver versus passenger sides.
Current maintenance procedures call for periodic scheduled inspections but vehicle brakes are inherently difficult to fully inspect since many critical components face each other (usually with only millimeter-sized gaps) and are not visible without invasive and costly manual inspection. Because of this, vehicle brakes are usually not disassembled and fully inspected more than twice a year and many problems can occur without notice between inspections. Additional evaluation methods are available such as performance-based brake testers (PBBT, including roller-dynamometers) and telematics but they too are often costly in terms of both time and money. Thus, the need exists for a low-cost, high-speed capability to monitor the condition of vehicle brakes and alert operators when problems are detected.
A number of prior patents have considered the use of acoustic information to analyze one or more aspects of brakes. For example, U.S. Pat. No. 5,372,221 uses active ultrasonic sources to measure brake pad thickness like the use of ultrasonic sounds in fetal examinations of human pregnancies. The system does not sense ultrasonic emissions from the brakes in operation. See also US Patent Publication No. 2004/0243358 and U.S. Pat. No. 9,482,301.
U.S. Pat. No. 8,078,353 measures road noise to predict driving conditions.
U.S. Pat. No. 8,152,246 discusses using microphones mounted on the vehicle to detect acoustic signatures of brakes with broken drive tendons, which will sound different than brakes that are working effectively. With a microphone on the vehicle, however, the system will have to account for environmental and road noises and need a separate device for each vehicle.